1. Field of the Invention
This invention relates to polymer blends comprising one or more electrically conductive conjugated backbone polymers and one or more non-conductive polymers, and to processes for the preparation of such blends. Another aspect of this invention relates to articles of manufacture fabricated totally or in part from the blend of this invention.
2. Prior Art
There are many techniques known in the art for forming polymer blends comprising electrically conductive fillers to give electrically conductive compositions. Typical conductive fillers used in the art are conductive carbons, graphites, metal fibers, metal flakes and metal powders. Various arts exist for compounding these materials into thermoplastics and thermosetting resins to give the desired combination of mechanical and electrical properties. (See A. Sternfield, Modern Plastics International, No. 7, 48 (1982).)
Because of the macroscopic nature of these electrically conductive fillers, the onset for three-dimensional conductivity in blends comprised of them typically occurs at some threshold loading, referred to as the percolation point. It is at this threshold loading level of the conductive filler that the conductive particles touch one another continuously throughout the blend in all three dimensions. One important aspect in the art is to devise conductive fillers and processing techniques to provide blends that exhibit desired electrical conductvities at minimum loading levels. Typically for conductive carbons with high surface areas (&gt;5m.sup.2 /g) , onsets for conductivity occur at loadings above 15 vol % carbon. With higher surface area carbons, onsets occur at 10-11 vol %, and with very high surface area carbons, onsets can occur at loadings as low as 5-7 vol %. (see B. Wessling, Kunstoffe, 76, 930 (1986)).
Another important aspect in the art is to modify the shape of the conductive fillers to provide fillers with anisotropic shapes. Such shaped fillers allow the use of lower loading to effect conductivity onsets in the blends compared to symmetrically shaped particles. For example, the use of small metal fibers with high aspect ratios may give certain blends that inhibit onsets for electrical conductivity at loadings as low as 2-4 vol. %. Systems comprising such anisotropically shaped fillers are typically difficult to process and often lead to non-reproducible results. (See K. Miyasaka, et al. J. Mat. Sci 17, 1610-1616 (1982).)
Inherently electrically conductive conjugated polymers are known in the art to be blendable with conventional thermoplastic and thermoset polymers. But, as with other conventional conductive fillers, blends containing inherently conductive polymers exhibit onsets for conductivity at loadings of about 7 vol % or above. See B. Wessling & H. Volk, Synthetic Metals, 15 183 (1986)) 16 127 (1986); 18, 671 (1987), and DE 3,440,617.
One technique recently developed for fabricating, conductive metal/polymer blends that contain exceptionally low metal loadings, entails melting a metal-polymer blend together until the metal is in a fibrous form. Such blends are described as having improved impart resistance and electrical and thermal conductivity. (D. E. Hudgin and M. A. SenSarzadih, U.S. Pat. No. 4,582,872).